UDP Question

An acquaintance suggested installing Peerblock
(for windoze). The array of blocked requests(?)
is enormous! Most of the blocked-by-Peerblock
UDP packets are from educational institutes.

There's even more blocked-by-Peerblock TCP
packets, mostly advertising; many just plain web
sites.

What are all these data 'pellets' being fired at my
PC? And - I presume - many others' PCs? They
come at rates of between 2-20 a minute, depend-
ing on what I'm doing on the www.

I guess they're small, but they must chew up one
or two kilobytes in a day. Maybe more?

Perry